Safety control circuit for heating device



NOV. 1, 1955 KOLB 2,722,595

SAFETY CONTROL CIRCUIT FOR HEATING DEVICE Filed Aug. 51, 1951 2 Sheets-Sheet l INVENTOR JOSEPH f. KOLB Nov. 1, 1955 J. E. KOLB SAFETY CONTROL CIRCUIT FOR HEATING DEVICE 2 Sheets-Sheet 2 Filed Aug. I51, 1951 Fig. 3

Rm 0 0 v1 W W m IH H O E J K United States Patent SAFETY CONTROL CIRCUIT FOR HEATING DEVICE Joseph E.Kolb, Pittsburgh, Pa., assignor to Edwin L. Wiegand Company, Pittsburgh, Pa., a cnrporation cf Pennsylvania Application August 31, 1951, Serial No. 244,499 3 Claims. '(Cl. 219-44) This invention pertains to a heating device and, more particularly, to a heating device including a container in which liquid or other material is heated, together with a heat supply means and a protective device and system for protecting the heating device and the container against damage from excessively high temperatures and operation of the heat supply means in the absence of material or liquid in the container, or at least a sufficient amount of material or liquid in the container to act as a modifying agent against excessively high temperatures. While the invention, for illustrative purposes, will be hereinafter described as applied to a hot water heater, it will be understood that it is not limited thereto but is capable of application to the heating of other materials and liquids. For example, the heating of air flowing through a conduit.

The protective device and system embodying the pres ent invention includes an electric circuit for controlling the operation of a heat supply means for a container, and a current conductor having a relatively high coeflicient of resistivity increase in response to rise in temperature forming a part of such electric circuit, the conductor being disposed in the container in .a position to be subject to the temperature modifying effect of the liquid or other material being heated, and being adapted when substantially or entirely relieved of the modifying effect .of the material ,or liquid, to increase in temperature and resistivity sufliciently to render the control circuit effective to cause the heat supply means to become inoperative.

It is one object of this invention to provide a protective device of such nature that a variation in electric currentbeyond predetermined limits will be eflective to render the heat supply means inoperative.

It is another object of this invention to provide a protective device and system for use with a heater of the type herein disclosed which will, under substantially any knowncondition, protect the material or liquid receiving container and the heat supply element from damage by excessive temperatures.

Various other objectives and advantageous features of the invention may be had from the following description, and .one embodiment thereof may be seen in the .ac-

companying drawings wherein similar characters of refer-- ences designate corresponding parts, and wherein:

Figure l is a fragmentary view, partly in elevation andpartly in section, showing one embodiment of a heat suply means and a protective device combined with a container.

Figure 2 is a bottom plan view of the apparatus shown in Figure 1, the container not being shown and the bottom cover for the heating element connections having been removed.

Figure 3 is a diagrammatic view showing a control circuit as applied to an electrical heat supply means and power circuit including multiple heating units.

Figure 4 is a view similar to Figure 3 'but showing the control circuit and power circuit combined through one electrical control. I

Figure 5 is a fragmentary view showing the protective device mounted separately with respect to the electrical heat supply means.

Referring to Figures 1 and 2 of the drawings, the heating apparatus shown for illustrative purposes includes a container 1 having an annular opening 2 in the bottom thereof, such opening being adapted to be filled by a block 3 having an outwardly extending flange 4 and a down wardly extending externally threaded shank 5, the flange 4 being adapted to overlie the circumferential edges .of theopening 2 on the inner side of the bottom of the container. An annular internally threaded ring 6 is adapted to cooperate with the external threads on the shank 5 of the block 3 and to overlie the circumferential edges on the outer side of the opening 2 in the bottom of the container. Sealing washers 7 are disposed between the flange 4 of the block 3 and the internal surface of the bottom of the container and between the ring 6 and the external surface of the bottom of the container whereby tightening of the ring 6 on the shank 5 of the block 3 will provide a liquid-tightseal between the block and the container opening 2.

Extending downwardly through the block 3 and in liquid-tight relation therewith are the terminal ends 8 of two heating elements 9 and 10 which include tubular sheaths 11 having therein spirally wound resistors 12, the resistors 12 being surrounded by an electrically insulating and heat conducting refractory material 13 compressed within the sheaths. Such spirally wound resistance elements are connected at their ends to terminals 14, and the corresponding terminal ends of the respective heating .ele-- ments are preferably connected by an electrically conducting car or strap 15 whereby a single current conducting lead will serve for such pair of terminal ends of the twoheating elements 9 and 10.

Acover .16, secured to the ring 6 by means of machine screws 17 is provided for protecting the terminal ends of the heating elements 9 and 10, and the electrical connections made thereto. A bottom closure 18 is provided, such bottom closure being secured to the cover 16 by machine screws 19 extending upwardly through the bottom cover and through internally threaded lugs 20 extending inwardly from the internal circumference of the cover 16.

Mounted above the heating elements 9 and 10, and preferably in a horimntal position, is an eletrical conductor 21 consisting of a tubular sheath containing a spirally wound resistance wire 22 embedded in electrically insulating and heat conducting refractory material ,23. Such conductor is generally U-shaped, and is provided with down-turned terminals 24 which extend downwardly through the block 3 and which are provided with terminal ends 25 for the connection of a suitable current conducting line thereto. in accordance with this invention, the resistance wire or element 22 is of a composition and nature to have a relatively high coeflicient of resistance change with change in temperature. As one illustrative example, an element consisting essentially of 72% nickel and the balance iron has been found satisfactory. In other words, as the temperature of the resistance wire rises the resistivity of the wire increases, and as the temperature of the wire decreases, or is modified by the cooling effect of an external cooling agent, the resistivity of the wire proportionately decreases. As will hereinafter he described the resistance wire or element is contained in and forms a part of a protective control circuit, with the operation or non-operation of the heat supply means including the heating elements 9 and 10 being normally dependent on the degree of resistivity of the element or wire 22.

Referring to Figures 3 and 4 of the drawings there are shown two circuits, Figure 3 showing a control circuit including a resistance 22 and a load circuit including a plurality of heating elements 12. Figure 4 shows a control circuit including a resistance 22, in combination with the load element 12.

Referring to the arrangement shown in Figure 3, electric current is supplied from a suitable source to the heating elements 12 through a circuit including the leads 26, 27, and 28 controlled by switches 29, 30, and 31, as will be apparent from the diagram, and in a manner well known in the art. The switches 29, 39, and 31 are actuated by energization of a relay coil 32.

The control circuit including the resistance 22 includes a line 33 leading from the lead 26 to the resistance 22 and a line 34 leading from the opposite end of the resistance 22 to a relay coil 35. Such relay coil 35 may be energized through a line 36, under the control of a manually actuated normally open switch 37, to the relay coil. When the manually actuated switch 37 is in closed position, current flows from the lead 26 through the line 33, resistance 22, line 34, relay coil 35, line 38, switch 37, and line 36, to lead 28.

A line 39 leads from the line 36 to a normally open switch 40 which, when the switch 40 is in closed position, connects the line 36 with the line 38 through line 41 on the opposite side of the switch 37 from the line 36. A line 42, under the control of the switch 43 leads from the line 36 to the relay coil 32 through line 44, and when the switch 43 is in closed position the relay coil 32 may be energized by a flow of current from lead 28 through lines 36 and 42, switch 43, line 44, relay coil 32, and line 45 leading from the relay coil 32 to the line 33 which, in turn, is connected to the lead 26. In the circuit shown in this figure, switches 40 and 43 are moved to closed position by operation of the relay coil 35, and switches 29, 39, and 31 are moved to closed position by operation of the relay coil 32.

In the operation of this circuit, energization of the relay 35 as hereinabove described by manual closing of the switch 37 will result in the switches 40 and 43 being moved to closed position. Movement of the switch 40 to closed position will, through lines 41 and 38, complete a circuit through the relay coil 35 to maintain such relay coil energized even though the manually operated switch 37 is permitted to move to open position. This is possible because the circuit is completed through conductor 34, resistor 22, and conductor 33. Closure of switch 43 will energize the relay coil 32 as hereinabove described to move the switches 29, 30, and 31 to closed position and complete the circuit to the heating elements 12.

In accordance with this invention, the resistance 22, being of such composition and nature as to have a relatively high coefficient of resistance change with change in temperature will normally permit flow of current of sufiicient amperage through the relay coil 35 to hold the switches 46 and 43 in closed position, whereby the relay coil 32 is energized and is effective to maintain the switches 29, 3t}, and 31 in closed position, and the heating elements 12 are thus maintained in operation. However, assuming that the liquid in the container 1 which normally surrounds the conductor 21 including the resistance unit 22 becomes depleted to such an extent that the conductor 21 is either substantially or completely out of the liquid, and thereby not subject to temperature modifying effect of such liquid, the resistance of the element 22 to the flow of current therethrough will immediately rise due to rise in temperature. When the resistance to fiow of current reaches a sufficient degree, the flow of current through the relay coil 35 will become insufficient to maintain the relay energized whereby the switches 40 and 43 will move to open position. Movement of the switch 43 to open position will result in the relay coil 32 becoming deenergized whereby the switches 29, 3t and 31 will move to open position and the circuit to the heating elements 12 will be interrupted and the heating elements 12 rendered inoperative to supply further heat, at least until the switch 37 is again manually 4 closed for repeated operation of the cycle hereinabove described.

For the purposes of illustration, assume that the relay coil 35 will operate the switches 40 and 43 when current is supplied thereto in the order of magnitude of two amperes, the resistance 22 being of such composition and nature that with its sheath temperature being less than for example 350 F. current of such order of magnitude will fiow therethrough. Should the conductor 21 and the resistance 22 contained therein become substantially or entirely relieved of the liquid acting as a temperature modifying agent, the temperature of the resistance 22 will immediately start to rise and the resistance of the unit become increasingly greater until the resistance offered by such unit becomes so great that the current flowing therethrough and to the relay coil 35 becomes less than two amperes say, for example, one ampere in magnitude and insutficient to maintain the relay energized and the switches 40 and 43 in closed position. Then, as hereinafter described, the relay coil 32 will become deenergized and the switches 29, 30, and 31 controlling operation of the heating units 12 will move to open position and render the heating elements inoperative to supply further heat to the container 1.

Referring to Figure 4 in which there is shown a single heating element 12, the switches 46 and 47 which control the flow of current from the leads 48 and 49 to the heating element 12, as well as the switch 50, are all moved to closed position simultaneously by a single relay coil 51. As shown in this figure, a line 52 leads from the lead 48 through the resistance 22 and line 53 to one side of the relay coil 51. A line 54 leads from the lead 49 to a manually operated normally open switch 55, and a line 56 leads from such switch to the relay 51. In addition, a line 57 leads from the contact 58 which is engaged by the switch when the switch is in closed position to the line 56 beyond the switch 55. In the operation of this control switch, manual closure of the switch will complete a circuit through the line 54, switch 55, line 56, relay coil 51, line 53, resistance 22, and line 52, to the lead 48, thereby energizing the relay coil 51 whereby the relay will be effective to simultaneously close the switch 50 to maintain the relay coil 51 energized by flow of current through the line 57 connected to the line 56 beyond the manually operated switch 55, and to also complete the circuit through the lead 48, switch 46, heating unit 12, switch 47, and lead 49, whereby the heating element becomes efiective. Similarly to the control circuit previously described in connection with Figure 3, should the temperature and resistance of the resistance element 22 rise suificiently due to substantial or complete uncovering of the conductor 21 by the liquid in the container 1, there will be insufficient current supplied to the relay coil 51 to maintain the relay coil energized and the switches 46, 47 and 50 in closed position, and the heating element 12 will therefore cease to operate to supply heat to the container 1.

In Figure 5 of the drawings there is shown a somewhat difierent arrangement of the conductor 21. As shown in this figure, the conductor 21 is extended through and secured to the side wall of the container 1 to lie in a position above the heating elements 9 and 10. While it is preferable, in the case of liquids that the conductor be disposed above the heating elements, the height of the conductor above the heating elements may be varied in accordance with the particular requirements of an installation. It is preferable that the conductor 21 containing the resistance 22 be so disposed, for example, horizontally, in the container so that the entire length of the conductor will emerge from the liquid substantially simultaneously, and thereby the temperature rise and resistivity increase take place throughout the whole length of the resistance unit rather than only a part of the length.

The protective device and system herein disclosed is such that it will protect the liquid receiving container and electric heater from damage by excessive tempera tures under substantially any known condition. The control circuit for the heat supply means is responsive to the temperature modifying effect of the liquid in the container, and therefore to the presence or absence of a determinable amount of liquid in such container. For example, should a suificient amount of the resistance be exposed to air by reason of lack of suificient liquid in the container, or should the heat supply means be placed in operation with no liquid in the container, the resistance 22 on operation of the heat supply means will rise in temperature and resistivity to a point to block the flow of current of suflicient amperage through the control circuit to maintain the heat supply means in operation. The resistance 22 is therefore of such nature that, While it will normally be effective to render the heat supply means inoperative before reaching a temperature at which the resistance fuses, should the resistance reach the fusion temperature, and all or a sufficient part of the resistance become fused, the heat supply means then cannot be again operated until the fused resistance has been replaced.

It will be understood that while electric heat supply means have been shown for illustrative purposes, the protective and control system is likewise adapted to use with other heat supply means, for example, where the relay forming a part of the protection circuit is arranged to open or close a valve to a liquid or a gas fuel burner. It will also be understood that the composition and nature of the resistance element 22 may be varied to obtain various degrees of resistivity coefiicient with respect to temperature change, as well as to adapt the resistance to electric currents of different magnitudesv What is claimed is:

1. Means for controlling the electrical heating of liquid, comprising a container for holding the liquid, a source of energy, an electrical heating resistor immersed in said liquid for heating the same, an electrical circuit including relay switch means connected to said heating resistor and a relay coil for closing said switch means to energize said resistor from said source of energy, an electrical control resistor in circuit with said relay coil and immersed in the container liquid above said heating resistor, both of said resistors being in thermal transfer relationship with the container liquid and subject to the heat modifying effects thereof, said control resistor having a relatively high coefficient of resistivity in response to its rise in temperature when the liquid level in the container is decreased sufiiciently to expose the same, a switch member in circuit with said relay coil for actuating said coil to close said relay switch means to energize said heating resistor and said control resistor, and a contact actuated by said relay coil and connected in multiple with said switch member, the current conducing capacity of said control resistor when exposed above the container liquid level, being insufiicient to maintain said relay coil effective to hold said switch means closed, thereby opening said switch means to shut off the flow of current to said heating resistor before damage is caused by lack of sufficient liquid in said container.

2. Means as defined in claim 1 wherein said switch member comprises an open biased switch.

3. Means as defined in claim 1 wherein said electrical circuit further includes a second relay coil under control of said first mentioned relay coil to effect operation of said second relay coil for controlling flow of current to said heating resistor.

References Cited in the file of this patent UNITED STATES PATENTS 915,974 Leonard Mar. 23, 1909 1,368,152 Huff Feb. 8, 1921 1,561,243 Keene Nov. 10, 1925 1,776,901 Essex et a1. Sept. 30, 1930 1,974,302 Finlayson Sept. 18, 1934 2,105,899 Wright Jan. 18, 1938 2,565,478 Crowley Aug. 28, 1951 2,581,212 Spooner Jan. 1, 1952 

